Control of paraffin deposition



March 29, 1955 e. VAN WILLIGEN CONTROL OF PARAFFIN DEPOSITION Filed July28, 1950 8 6 Z R I 2 7M 3 M 20 I PRODUCING ZONE.

INVENTOR GERRIT VAN wuueau BY: k

HIS ATTORNEY United States Patent '0 CONTROL OF PARAFFIN DEPOSITIONGeri-it Van Willigen, The Hague, Netherlands, assignor to ShellDevelopment Company, San Francisco, Cal1f., a corporation of DelawareApplication July 28, 1950, Serial No. 176,378

3 Claims. (Cl. 103-1) This invention relates to the control of paraflindeposition in a well from which a paraflin-containing 0111s beingpumped, and pertains more particularly to a method and apparatus forpreventing deposition of paraflin on a string of sucker rods beingemployed to actuate a well pump.

In producing wells the oil is usually lifted to the surface through atubing string having at its bottom end a pump, generally a plunger-typepump, which is rec1procated from the surface by a string of sucker rodsmoving up and down inside the tubing.

If the oil to be lifted is viscous, the sucker rods will encounterconsiderable resistance in their up-and-down, motion, which resistancewill in particular limit the speed of the downward stroke of the rodsand plunger and, consequently, the pumping rate. With a paraffin-baseoil, paraflin may be depositedon the string of rods, and also on theinner side of the tubing string. This results in a diminution of theannular space between rods and tubing, i. e. of the passage throughwhich the oil is lifted, so that, since the pump stroke and consequentlythe quantity of oil displaced are constant, the rate of flow increases.a result the flow resistance also increases, which lIl turn creates ademand for more energy from the engine which reciprocates the string ofsucker rods. As a matter of fact, paraffin deposits call for frequentcleaning of the tubing and sucker rod strings, which operation involvesconsiderable loss of time and expense.

It is therefore a primary object of the present invention to provide amethod and means for controlling the deposition of paraffin on theproducing equipment within a well and for preventing the accumulation ofparaflin on the string of sucker rods being used to operate the wellpump.

It is also an object of this invention to provide a method and anapparatus for the removal of accumulated paraffin deposits from wellequipment by the circulation of a paralfin solvent through the producingequipment.

Additional objects and advantages will become apparent from a study ofthe following description when considered in conjunction with theaccompanying drawing, wherein the single figure gives a longitudinalview, partly in cross section, of the producing equipment employed in awell being produced by a reciprocating pump.

Referring to the drawing, a well borehole is shown lined with a stringof casing 11 which is closed at the top by a conventional casing head12. Depending from the casing head 12 within the casing 11 are twoconcentric strings of tubing which will be hereinafter identified as theouter tubing string 13 and the inner tubing string 14. The inner tubing14 normally extends to the bottom of the well or to a pointsubstantially adjacent the producing zone of the Well.

A conventional plunger pump 15 is anchored in the inner tubing 14 in amanner well known to the art, said pump 15 being preferably anchored atthe level of the producing zone. At this point the inside of the casing11 is in communication with the space outside thereof through a seriesof perforations 16 in said casing. The pump is actuated by a string ofsucker rods 17 extending up through the inner tubing 14 and passing in afluidtight manner through the casing head 12, where said sucker rodstring is reciprocated by suitable prime mover means (not shown) locatedat the surface.

At the surface the casing head 12 is provided with suitable conduitmeans for introducing or discharging fluids from the well. Thus, theinner tubing string is provided with an outlet conduit 18, the annularspace 19 between the outer and inner tubings 13 and 14 is equipped withdischarge conduits 20 and 21, and the annular space 22 between thecasing 11 and the outer tubing 13 may be provided with a conduit 23. Theflow of fluids through conduits 18, 20, 21 and 23 is controlled byvalves 24, 25, 26 and 27.

The length of the outer tubing string 13 may vary and depends upon suchwell characteristics as well depth, well temperature, composition of theoil being pumped, paraffin content of the oil, etc. In general, theouter tubing 13 extends from the casing head 12 down to the lowest pointin the well at which paraflin is known to accumulate on the innersurface of the inner tubing string 14.

A fluidtight seal is formed between the bottom of the outer tubing 13and the outer wall of the inner tubing 14 in any suitable manner wellknown to the art. For example, a conventional packer can be employed oran annular plate may be welded in place. In the latter case it would benecessary to insert or pull both strings of tubing 13 and 14 from thewell together. To obviate the necessity of pulling the outer tubing 13when a pump is being replaced, the lower end of the outer tubing 13 ispreferably provided with a shoe 28 having an internal seating face 30 ofan annular ring 31 carried on the outer surface of the inner tubing 14.When the seating faces 29 and 30 are in engagement a fluidtight seal isformed between the lower end of the outer tubing 13 and the outer wallof the inner tubing 14.

The inner tubing string 14 is provided with fluid ports or perforations32 in communication between the bore of the inner tubing and the annularspace 19 between the tubings 13 and 14 above the ring 31. In operation,the inner tubing 14 may be filled with a gas or a stagnant liquid, saidfluid being introduced through conduit 18. Thus, a considerable lengthof the reciprocating sucker rods 17, which actuate the pump 15, move inthe inner tubing 14 filled with gas or stagnant liquid so that theyencounter considerably less resistance than if they had to move in theoil being pumped, especially if this oil is viscous.

The oil from the formation flows into the casing 11 through perforations16 and thence into the pump 15. The reciprocating pump 15 then lifts thefluid up the inner tubing 14 until it reaches the slots 32 at whichpoint the fluid flows into the annular space 19 between the inner andouter tubings 14 and 13 and is lifted therein to the head of the wellwhere it is discharged through conduit 20 or 21. Owing to the fact thatthe annular passage 19 is considerably larger than the bore of the innertubing 14, paraflin deposits which are formed in this annular passage 19on the outer surface of the inner tubing 14 or on the inner surface ofthe outer tubing 13 cause much less trouble than when the well isproduced through a single tubing.

Since the outer tubing 13 extends below the point at which paraflindeposits are formed, no paraflin becomes deposited on the inner surfaceof the inner tubing 14 or on the sucker rods 17. Below the perforations32 the temperature of the oil is sufficiently high to preventdepositions of paraflin, while above the perforations the gas orstagnant liquid prevents deposition by preventing the rise of oil to anyconsiderable height above said perforations. As a result, less energy isrequired by the prime mover to reciprocate the pump and, hence, the rateof pumping may be increased. in addition, the arrangement according tothis invention has the advantage that, when the tubing string has to becleaned, a cleansing medium, for instance steam, hot oil, hot water,etc., can be injected into the inner tubing 14, to emerge again throughthe annular space between inner and outer tubing 19, thus freeing thisannular space from parafiin. This treat-. ment can therefore be carriedout without having to pull the system of pump and rods to the surface.It is also possible to separate a portion of the lifted oil, to heatthis portion in a heat-exchanger, and then to inject it into the innertubing 14. This hot oil is then lifted again, together with the oildelivered by the pump, through the annular space 19, so that theproduction process need not be interrupted. The path of the heated oilcan also be reversed, whereby the mixture of hot oil and oil deliveredby the pump is lifted) through the inner tubing 14.

It is not necessary, as a rule, to install a double tubing over thewhole length of the tubing string, since, especially in the case of deepwells, owing to the high temperatures which prevail at greater depths,the fluidity of the oil is greater, so that it does not offer such greatresistance as when it is more viscous; nor will paraffin be deposited atelevated temperature as long as this temperature lies above the settingpoint. Consequently, the double tubing need only be installed to a depthat which the temperature is such as to cause the above-mentioneddifliculties. The double tubing arrangement is also extremely suitablefor the injection of chemicals, which are very often applied to preventformation of emulsion and paratfin deposits, in the same way asdescribed above with reference to a cleansing medium. In this case it isoften advisable that the double tubing extends down to very near theump.

p If a liquid, such as hot oil, hot water, or a solution of chemicals orparaflin solvents, is to be circulated with the oil for cleaning thetubing strings 13 and 14, the liquid may be injected through conduit 18.This liquid is passed down the inner tubing 14, through slots 32together with the oil being delivered by the pump 15, and up the annularspace 19 to be discharged at the well head through conduit 21. It is tobe noted that only a relatively small amount of a solvent is needed withthe present apparatus as it is confined to the portion of the tubingstrings 13 and 14 in which the paraflin deposits occur and at no timecomes in contact with the producing formation. The cleaning liquid canalso be circulated in the reverse direction in the present apparatus byinjecting the liquid through conduit 20 into the annular space 19 andflowing it through perforations 32 and up the bore of the inner tubing14 along with oil to be discharged through conduit 18.

I claim as my invention:

1. An apparatus for producing an oil well, comprising a first tubingstring extending from the surface of the ground to the oil producingreservoir, a second tubing string of larger diameter surrounding saidfirst tubing string in spaced relationship therewith and extending intothe well to a depth below that of the zone in which substantialquantities of paraflin are deposited from the well fluid, said secondstring being shorter than said first string, closure means within thelower end of said second tubing string for closing the annular spacebetween said first and second tubing strings, fluid discharge port meansthrough the wall of said second tubing string near the upper endthereof, fluid port means through the wall of said first tubing abovesaid closure means, pump means carried at the lower end of said firsttubing string, a string of sucker rods secured to the pump means andextending to the surface within said first tubing string forreciprocating said pump means, means at the surface closing the annularspace between the first and the second strings, and means for supplyingto said first string a fluid at a pressure sufiicient to prevent the oilfrom rising within said first string to a level appreciably higher thanthat of said fluid port means when said pump means is operated.

2. An apparatus for producing an oil well, comprising a first tubingstring extending from the surface of the ground to the oil producingreservoir, a second tubing string of larger diameter surrounding saidfirst tubing string in spaced relationship therewith and extending intothe well to a depth below that of the zone in which substantialquantities of paraffin are deposited from the well fluid, said secondstring being shorter than said first string, a first annular membersecured to the inner wall of said second tubing string, a second annularmember carried outwardly on said first tubing string adapted to coactwith said first annular member to close the annular space between saidfirst and second tubing strings, fluid discharge port means through thewall of said second tubing string near the upper end thereof, aplurality of fluid ports through the wall of said first tubing abovesaid annular members, pump means carried at the lower end of said firsttubing string, a string of sucker rods secured to the pump means andextending to the surface within said first tubing string forreciprocating said pump, means at the surface closing the annular spacebetween the first and the second strings, and means for supplying tosaid first string a fluid at a pressure suflicient to prevent the oilfrom rising within said first string to a level appreciably higher thanthat of said ports when said pump means is operated.

3. An apparatus for producing an oil well, comprising a first tubingstring extending from the surface of the ground to the oil producingreservoir, a second tubing string of larger diameter surrounding saidfirst tubing string in spaced relationship therewith and extending intothe well to a depth below that of the zone in which substantialquantities of paraflin are deposited from the well fluid, said secondstring being shorter than said first string, closure means within thelower end of said second tubing string for closing the annular spacebetween said first and second tubing strings, fluid discharge port meansthrough the wall of said second tubing string near the upper endthereof, fluid port means through the wall of said first tubing stringabove said closure means, top closure means closing the top of saidfirst tubing string to form a fluidtight chamber in said first tubingstring above said fluid port means therein, said first tubing stringbeing adapted to be filled with a stagnant fluid, normally-closed portmeans through the wall of said first tubing string for introducing saidfluid, pump means carried at the lower end of said first tubing string,and a string of sucker rods secured to the pump means and extending tothe surface within said first tubing string for reciprocating said pumpmeans.

References Cited in the file of this patent UNITED STATES PATENTS1,012,777 Wigle Dec. 26, 1911 2,020,550 Herrick Nov. 12, 1935 2,083,799Roberts June 15, 1937 2,368,777 Price Feb. 6, 1945 2,394,189 KaufmanFeb. 5, 1946

1. AN APPARATUS FOR PRODUCING AN OIL WELL, COMPRISING A FIRST TUBINGSTRING EXTENDING FROM THE SURFACE OF THE GROUND TO THE OIL PRODUCINGRESERVOIR, A SECOND TUBING STRING OF LARGER DIAMETER SURROUNDING SAIDFIRST TUBING STRING IN SPACED RELATIONSHIP THEREWITH AND EXTENDING INTOXXLE WELL TO A DEPTH BELOW THAT OF THE ZONE IN WHICH SUBXXANTIALQUANTITIES OF PARAFFIN ARE DEPOSITED FROM THE WELL CLOSURE MEANS WITHINTHE LOWER END OF SAID SECOND TUBING STRING FOR CLOSING THE ANNULAR SPACEBETWEEN SAID FIRST AND SECOND TUBING STRINGS, FLUID DISCHARGE PORT MEANSTHROUGH THE WALL OF SAID SECOND TUBING STRING NEAR THE UPPER ENDTHEREOF, FLUID PORT MEANS THROUGH THE WALL OF SAID FIRST TUBING ABOVESAID CLOSURE MEANS, PUMP MEANS CARRIED AT THE LOWER END OF SAID FIRSTTUBING STRING, A STRING OF SUCKER RODS SECURED TO THE PUMP MEANS ANDEXTENDING TO THE SURFACE WITHIN FIRST TUBING STRING FOR RECIPROCATINGSAID PUMP MEANS, MEANS AT THE SURFACE CLOSING THE ANNULAR SPACE BETWEENTHE FIRST AND THE SECOND STRINGS, AND MEANS CIENT TO PREVENT THE OILFROM RISING WITHIN SAID FIRST STRING TO A LEVEL APPRECIABLY HIGHER THANTHAT OF SAID FLUID PORT MEANS WHEN SAID PUMP MEANS IS OPERATED.